de Broglie wavelength reduction for a multiphoton wavepacket

An experiment is proposed that permits the observation of the reduced de Broglie wavelengths of two and four-photon wave packets using present technology. It is suggested to use a Mach-Zehnder setup and feed both input ports with light generated by a single non-degenerate down-conversion source. The strong quantum correlations of the light in conjunction with boson-enhancement at the input beam splitter allow to detect a two- and fourfold decrease in the observed de Broglie wavelength with perfect visibility. This allows a reduction of the observed de Broglie wavelength below the wavelength of the source.